(case involved USDA-administered Consolidated Farm and Rural Development Act and dispute between two water service providers over which is entitled to serve customers located in and around Guthrie, OK; plaintiff claimed right to serve based in state law and that it was protected from competition from encroaching districts by 7 U.S.C. §1926(b); trial court ruled for plaintiff and appellate court affirmed because plaintiff established continued indebtedness to USDA and that plaintiff “made service available” in satisfaction of statute).